Most common heating devices used currently in this country is a gas burning forced air furnace. Such a furnace, as is well known, uses a gas burner, a plenum or heat chamber into which the heated gas passes, a forced air blower, typically having from one-half horsepower up to one horsepower, and of course, associated temperature sensitive switches for on-off switching of the burner and the forced air blower in response to temperatures within the plenum, or furnace heating chamber, the two terms being used interchangeably herein, and the temperature in the associated room air space.
The operation of this conventional unit is well known but will be briefly described herein. Typically the associated temperature sensitive switch responsive to the air temperature in the plenum chamber is set to actuate at from 180.degree. F. to 200.degree. F. It is set at this temperature, which of course is considerably higher than the room temperature, because the warmed air within the plenum chamber must at least be this hot or else the large forced air blower will immediately cool it upon its operation, thereby decreasing the heating value of the warmed air. As a result, the forced air blower does not start until the air within the plenum chamber is much, much hotter than the desired room temperature. Likewise, the temperature sensed for shut-off of the forced air blower is also considerably higher than the desired room temperature in order that the forced air blower shuts off before the air within the plenum chamber cools to the point at which continual forcing of the air into the home air flow paths causes cooling. Typical blower activation and shut-off temperatures are from 180.degree. F. to 200.degree. F.
The result of this operation is that there is considerable warmed air in the plenum chamber available for displacement in to the room air space before the forced air blower comes on and there is also much available warmed air remaining in the plenum chamber and the duct work after the forced air blower shuts off. This warmed air is currently not being utilized and as a result, considerable energy is wasted.
Another disadvantage of operation of the present system is that it provides for continually fluctuating room temperatures. Say, for example, the room thermostat is set at 70.degree. F., but the room has actually cooled to 66.degree. to 67.degree. F. The room thermostat actuates the burner which will require generally at least two minutes or more to heat to the 180.degree. F. to 200.degree. F. plenum temperature at which the large furnace blower is activated. Meanwhile, the room temperature will drop an additional one to two degrees, i.e., 65.degree. to 66.degree. F. When it is activated, the forced air blower forces hot air from the plenum pushing the hot air through the duct work into the room air space. When the room temperature reaches 72.degree. to 73.degree. F. the burner shuts off. However, air within the plenum chamber is still above the 180.degree. F. activation temperature for the forced air blower which will continue to operate, usually sending the room temperature up to 75.degree. to 76.degree. F. before it shuts off. Thus, as can be seen, there are extremes in room temperature from a low of about 65.degree. F. to a high of as much as 75.degree. to 76.degree. F.
The reason for this room temperature variance is, of necessity, the fact that the large forced air blower for the furnace is set for on-off operation at a temperature typically within the range of 180.degree. F. to 200.degree. F.
Accordingly, it is an object of the present invention to provide a method whereby the warmed air present in the plenum chamber of a gas burning forced air furnace which is hotter than the room temperature but lower than the forced air blower activation temperature, will be maximized and used before the forced air blower turns on, and wherein the warmed air in the plenum chamber after the air blower shuts off will still be utilized until it no longer has significant heat value in comparison with the desired set temperature for a room thermostat.
Accordingly, it is another object of this invention to provide a method and apparatus which allows for use of utilized warm, hot air trapped in the plenum chamber of a furnace which is otherwise wasted, thereby increasing fuel efficiency and in addition, allowing for more constant room temperature control.
The method of accomplishing these and other objects of the invention will become apparent from the following detailed description of the invention.